1. Field of Invention
The present invention relates to a method of depositing a metallic film on a substrate using atomic layer deposition (ALD). This method uses a carrier gas to deposit a selected source metal on a substrate in a reaction chamber. Excess source metal is removed using a pulse of an inert gas such as nitrogen. A reducing agent is then pulsed into the reaction chamber followed by a pulse of purge gas such as nitrogen. This series of steps is then repeated for other selected source metals of interest, for each layer of source metal that is to be deposited onto the substrate. This process may be used for the deposition of conformal seed layers for subsequent electrodeposition of thicker films for microelectronic interconnect applications.
2. Description of The Prior Art
Electrodeposition of copper for the fabrication of microelectronic device interconnects has been used in the prior art. Prior to electrodeposition or electroplating, a wafer requires a thin layer of copper (Cu) which is known as a seed layer. Versions of sputtering have been employed in the prior art to deposit seed layers. As the dimensions of microelectronic devices shrink, new ways are needed of depositing a uniform seed layer in high aspect ratio trenches and vias of damascene structures. Prior art in the ALD of copper films consists of using a platinum under layer with hydrogen as a reducing agent, or elemental zinc vapor as a reducing agent. The copper film produced with these methods has high resistivity, rough texture, and contains large amounts of impurities. Hence, these methods are not suitable for microelectronic applications.
Chemical vapor deposition techniques have been used to deposit metallic substances, such as copper, on substrates. In CVD methods all of the reactants are present in the reaction chamber at a single time. In contrast to CVD methods, in ALD methods a single source metal is introduced into a reaction chamber at a given time for deposition. The deposition temperatures required for ALD are slightly less than those required for CVD. With the advent of nanotechnology, there is an increasing need to develop methods for depositing nanoscale metallic films on substrates for use in producing items such as state of the art microelectronic devices, circuit boards, and architectural coatings.
The present invention provides an ALD method for sequentially depositing monolayers of highly conformal, continuous smooth metallic films. The thickness of the deposition can be controlled by controlling the number of deposition cycles. The chemistry employed for ALD can also be used for CVD of metallic films, where are the chemicals will be introduced to the reaction cell at the same time.